The present invention relates to a device and method for temporarily identifying tube rows on a tubesheet. In a tube and shell heat exchanger, such as a vertical tube chemical reactor, there are situations in which it is helpful to be able to identify the tubes, such as when the tubes are being loaded with catalyst, unloaded, blown down, cleaned, inspected, repaired, or pressure tested. This is usually done by numbering the rows and then numbering the tubes within a row. Workers often identify the rows temporarily by marking the row numbers on the tubesheet with chalk, but this is time consuming, leaves undesirable material on the tubesheet, the markings can be scuffed or erased when walking over them, and there is the possibility of dropping a piece of chalk down one of the tubes, which would be very undesirable. It is also known to number the rows temporarily using paint and ink, which has essentially the same problems as chalk. Rows also can be marked permanently by stamping, welding, etching and adding other welded pieces like nuts, bolts or pins, but such permanent markings often are not present.